Telephone system



Dec. 14, 1937. A. B. SPERRY 2,102,137

, TELEPI'IONEv SYSTEM Filed June 25, 1936 2 Sheets-Sheet l lllllINVENTOR By A. B. SPERRY A TORN V Dec. 14, 1937. A. B. SPERR-Y 2,102,137

' TELEPHONE SYSTEM Filed June 25, 1936 I 2 Sheets-Sheet 2 OFF/CE 2 FIG-2 mun/rs INVENTOR A. B. SPERRV ATTOR/V r Patented Dec. 14, 1937 UNITEDSTATES PATENT OFFICE TELEPHONE SYSTEM Arthur B. Sperry, New York, N. Y.,assignor'to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application June 25, 1936, Serial No. 87,184

6 Claims.

'5 liability of double connections and to otherwise improve theefiiciency of the switching equipment in telephone systems.

Where interofiice trunks in a dial system are used for completing callsin both'directions, it is 10 necessary to provide busy indicating meansat each end of the trunk, which means is rendered effective as soon aspossible after seizure of the trunk at the opposite end. Between thetime a trunk is seized at one end and the time that the busy indicatingmeans at the opposite end has become effective, the trunk is subject todouble seizure. Various arrangements have heretofore been employed forreducing this unguarded interval. The trunk may normally be connected at2 each end to the line relay of an associated incoming selector in whichcase the busy guard awaits the operation of both the line relay and therelease relay of the selector. Or the trunk may normally be connected ateach end to an incoming repeater, the line relay of whichis immediatelyeffective upon seizure at the opposite end to establish a guard toprevent a double connection, the line relay also being effective torepeat impulses to the incoming selector. 30 According to this inventionthe intervalduring which a two-way trunk is unguarded at one end, afterseizure at the opposite end, is greatly reduced by an arrangementcomprising a line or trunk relay, normally connected to the trunk and 5operatively responsive to seizure of the trunk at the distant end, and.a switching relay for transferring the trunk from the windings of thetrunk relay to the windings of the line relay of the associated incomingselector switch. Operation of 40 the trunk relay upon seizure of thetrunk at the distant end, immediately connects a guarding potential tothe test terminal of the trunk in the banks of selectors having accessthereto and closes a local circuit for operating the line relay 45 ofthe incoming selector. The resulting operation of the release relay, andconnection of ground potential to the sleeve conductor, of the selectorswitch causes the operation of the switching relay so as to connect thetrunk to the line relay of the 50 incoming selector and make this linerelay directly responsive to dial impulses incoming over thetrunk. Theinvention. will be readily understood by considering a telephone systemin which it is em- 55 bodied, one such system being illustratedschematically in the drawings which form a part of this specification.The invention is not limited in its application tothe system shown inthe drawings butmaybe applied to any system employing automatic switchesand two-way trunks 5 for the completion of interoflice connections.

Referring to the drawings:

Fig. 1 shows an automatic telephone office comprising subscribers linesLI and L2, a line finder switch LB! and an associated selector switchSI, 10

a two-way trunk circuit TI and an associated incoming selector switchISI and a connector switch Cl; and

Fig. 2 shows another automatic office comprising subscribers lines L3and L4, a line finder LF2 15.

and an associated selector switch S2, a two-way trunk circuit T2and anassociated incomingselector switch IS2, and aconnector switch C2.

The trunk circuits TI and T2 are alike and the corresponding switches inthe two ofiicesmay also be similar. The finder, selector and connectorswitches are of the type usually known as step-bysteptwo-motion'switches. For a description of theconstruction of suchswitches and their operation as selectors and connectors, reference maybe had to Automatic Telephony by Smith and Campbell, second edition,pages 53 to 65 inclusive. For a description of the operation of suchswitches when used as line finders, reference may be had to Patent1,799,654, granted to R. L. Stokely, April 7, 1931. The switches LFI,LFZ, S1, S2, ISI and CI are each represented by a set of brushes and asingle set of terminals, none of the associated circuit equipment beingshown. The banks of the incoming selector switch IS2 and connectorswitch C2 are also represented by single sets of terminals; but thecircuit equipment associated with the selector IS2 is shown in detail,and as much of the circuit equipment associated with the connector C2 isshown as is necessary for a clear and complete description of thesystem.

Consider first a call from station A of line Ll in ofiice I to station Cof line L3 in ofiice 2, the call being completed over trunk T. Assumingthe line finder LFI to have been operated, in re- 5 sponse to removal ofthe receiver at station A, to connect line Ll with the associatedselector SI, and the selector SI to have been selectively operated underthe control of the dial (not shown) at the calling station to extend theconnection to the trunk equipment Tl, a circuit for operating relay I1is closed from the ground potential temporarily connected to the sleevebrush of the selector, over sleeve conductor l3, through back contactsof relays 2| and 22, and the winding of relay 11 in 5 parallel with thebiasing winding of relay I9; and a circuit for operating relay I4 isclosed through the windings of relay I4, normally closed contacts ofrelay I9, conductors II and I2, the two upper brushes of switches SI andLFI, and the conductors of line LI. Relay I4 closes at its lower frontcontact a circuit for operating relay I5 and relay I 5 closes at itsupper contact a circuit for operating relay I6. Each of relays I5 and I6con nects ground to the sleeve conductor I3 so as to hold the precedingline finder and selector switches in usual manner. This ground isfurther extended through the left back contact of relay 2| and next tothe outermost back contact of relay 22 for holding relay I1 and formaintaining the energization of the biasing winding of polarized relayI9. Relay I1 disconnects the conductors of trunk T from the windings oftrunk relay 2|; and, with both of relays I4 and I1 operated, the upperwinding of relay I9 is bridged across the trunk T, thereby completing acircuit through back contacts of relays 31 and 42 of trunk equipment T2for operating trunk relay 4|. The current in this circuit is in theopposite direction to that required for causing the operation of relayI9. At its right front contact, relay 4| connects ground to sleeveconductor 33 to guard the trunk equipment T2 from being seized byselector S2 or any other selector having access to this trunk. At itsleft front contact, relay 4| closes a circuit, over conductors 41 and 48and through back contacts of relay 51 of incoming selector 162, foroperating the line relay 5| of the incoming selector. Relay 5| closes acircuit for operating relay 52 and relay 52 connects ground through itslower front contact to sleeve conductor 49 to operate relay 42 of thetrunk equipment T2. Relay 42 transfers the conductors of trunk T fromthe windings of trunk relay 4| to the windings of line relay 5| ofselector 1S2. Relay 4| then releases so that relay 5| is held operatedunder the sole control of relay I4 of trunk equipment TI. When relay 4|releases, the sleeve conductor 33 is connected through the back contactof relay 4| to ground at the outer front contact of relay 42, therebycontinuing the guard against seizure of trunk T by a selector in ofiice2.

When the calling subscriber dials the next digit of the calledsubscribers number, relay I4 is alternately released and reoperated inresponse to each impulse in usual manner thereby opening and closing thebridge across trunk T to cause a corresponding release and reoperationof relay 5| of incoming selector 1S2 in office 2. Therelease of relayI4, in response to the first impulse, also closes a circuit foroperating relay I8; and relay I8, which is slow in releasing, remainsoperated to improve the impulse circuit over trunk T while all of theimpulses in the train are being repeated by relay I4. Relays I5 and I6are also slow in releasing so that ground is not disconnected from thesleeve conductor I3 while relay I4 is responding to dial impulses. Eachrelease of relay 5| of selector 1S2 closes a circuit through the windingof slow-to-release relay 53 and the winding of the vertical steppingmagnet 54. Each operation of magnet 54 steps the brushes of switch 132up one level, relay 53 remaining operated until all of the impulses inthe train have been received. Relay 53, being slow in releasing, remainsoperated during the response of relay 5| to dial impulses. When theshaft and brushes are moved out of normal position, the verticaloil-normal springs VON are actuated thereby closing a circuit, throughthe upper contacts of these springs and the front contact of relay 53,for operating relay 55. When relay 53 releases after the brushes havebeen stepped up to the desired level, relay 55 is held operated throughthe back contact of the rotary stepping magnet 56, the outer frontcontact of relay 55, and the middle lower back contact of relay 51; anda circuit for operating magnet 55 is closed through the inner frontcontact of relay 55, and through the back contact of relay 53 to groundat the lower front contact of relay 52. When magnet 55 operates, thebrushes are stepped into contact with the first set of terminals in theselected level. The operation of magnet 55 causes the release of relay55; and relay 55 in turn causes the release of magnet 56. If the firstset of terminals is idle, relay 51 is operated by the current in acircuit from battery through the winding of relay 55, upper contact ofthe VON springs, back contact of magnet 56, winding of relay 51, uppercontact of the 11th rotary step springs, to ground at the lower frontcontact of relay 52. Relay 55, being marginal, does not operate inseries with relay 51. If, however, the first set of terminals is guardedby ground potential connected to the sleeve terminal, this ground isconnected through the sleeve brush and lowermost back contact of relay51 to shortcircuit the winding of relay 51 and cause the reoperation ofrelay 55; relay 55 then again closes the circuit for operating magnet 56and the brushes are stepped to the next set of terminals. This steppingoperation is repeated until an idle set of terminals is encountered atwhich time relay 51 operates as above described. At its upper and innerlower front contacts, relay 51 extends the connection from trunk T overconductors SI and 62 to the line relay 54 of the connector switch C2. Atthe lowermost front contact of relay 51, ground at the lower frontcontact of relay 52 is temporarily extended to the sleeve terminal ofthe selected set to prevent seizure of the same connector by any otherhunting selector. The operation of relay 51 also causes the release ofrelays 5| and 52. The operation of the line relay 84 of connector C2closes a a circuit for operating the release relay 65; and relay 65connects ground to sleeve conductor 63 to hold relay 51 of selector I82and to hold relay 42 of trunk equipment T2. The dial impulses,

corresponding to the last two digits of the called 1.

subscribers number, are repeated by relay I4 of trunk equipment TI torelay 54 of switch C2 and connection with the line L3 is therebyefiected in usual manner. When the called subscriber answers, the lineL3 is connected to relay 59, and

the operation of relay 69 reverses the connection of the windings ofrelay 64 with respect to conductors BI and 52 so that the current overthese conductors, the trunk T, and through the upper winding of relay I9of trunk equipment T2 is reversed to cause the operation of relay I9.Relay I9, in turn, reverses the connection of the windings of relay I4with respect to conductors I I and I2 to control metering or any otherfunction dependent upon answer of the called subscriber. Conversationthen takes place, the talking currents being transmitted throughcondensers 25 of trunk equipment TI, and condensers 10 of connector C2.If the called subscriber replaces the receiver, relay 69 releases, thusrestoring the direction of current over trunk T to cause the release ofrelay I9 of trunk equipment TI. When the calling subscriber replaces thereceiver, relay I4 releases. The release of relay I4 causes the releaseof relays I5, .I 6 and I1 and opens the bridge across the conductors oftrunk T to cause the release of relay 64 of switch C2 and the release ofrelay iii, if at that time operated. The release of relays l 5 and i6disconnects ground potential from sleeve conductor l3 thereby causingthe return of switches LFI and SI to normal in usual manner. The releaseof relay l1 reconnects the conductors of trunk T to the windings ofrelay 2|. The aforementioned release of relay 64 of switch C2 causes therelease of relay 65. Relay 65 disconnects ground potential from thesleeve conductor 63 to cause the release of relays 51 and 42 and alsocauses the operation of the release magnet (not shown) to return theswitch 02 to normal. The release of relay 42 reconnects the conductorsof trunk T to the windings of relay M and disconnects the guardingground potential from conductor 33 and the terminals to which thisconductor is connected. The release of relays EI, 52 and 51 closes acircuit for operating release magnet 59; and switch 1S2 is restored tonormal in usual manner.

On a call from station D to station E, the line L4 is extended throughthe line finder switch LF2, selector S2, trunk equipment T2, trunk T,trunk equipment Tl, incoming selector IS], and connector Cl to line L2.The operation of trunk equipment T2 is like that of equipment Ti, andthe operation of trunk equipment TI is like that of equipment T2, on thecall from station A to station C hereinbefore described.

Although the system illustrated herein employs switches of thestep-by-step type, it is understood that any suitable kind of switch maybe used. It is further understood that the invention may be applied tosystems in which operators take part inthe establishment of connections.

What is claimed is;

1. In a telephone system,'a two-way trunk line, meansat each end of saidtrunk for seizing said trunk on outgoing calls, a trunk relay at eachend of said trunk, said relays being normally bridged across theconductors of said trunk for operation upon seizure of the trunk at theopposite end, a selector at one end of the trunk for use in completingcalls incoming over said trunk, a line relay for said selector, acircuit closed by the operation of the trunk relay at said one end ofthe trunk for operating said line relay, and means responsive to theoperation of said line relay for transferring the conductors of saidtrunk from said trunk relay to said line relay.

2. In a telephone system, a trunk, means at each end of said trunk forseizing said trunk, a trunk relay normally connected to one end of saidtrunk for operation upon seizure of said trunk at the opposite end, saidrelay when operated being effective to guard said trunk against seizureat said one end, an incoming selector at said one end of the trunk foruse in completing calls incoming over said trunk, a line relay for saidselector, a circuit closed by the operation of said trunk relay foroperating said line relay, and means responsive to the operation of saidline relay for transferring the trunk from said trunk relay to said linerelay.

3; In a telephone system, a trunk, means at each end of said trunk forseizing said trunk, a trunk relay normally connected to one end of saidtrunk for operation upon seizure of said trunk at the opposite end, saidrelay when operated being eiTective to guard said trunk against seizureat said one end, an incoming selector at said one end of the trunk foruse in completing calls incoming over said trunk, a line relay for saidselector, a circuit closed by the operation of said trunk relay foroperating said line relay, and means responsive to the operation of saidline relay for transferring the trunk from said trunk relay to said linerelay and forv guarding said trunk against seizure at said one end.

4. In a telephone system, a two-Way trunk, like means at each end ofsaid trunk for seizing said trunk on an outgoing call, a trunk relay ateach end of said trunk, each of the trunk relays being normally bridgedacross the conductors of the trunk for operation in response to seizureof the trunk at the opposite end, a selector at each end of the trunkfor use in completing calls incoming over the trunk, a line relay foreach of the selectors, contacts on each of said trunk relays forguarding the trunk against seizure at the end at which the relay islocated and for operating the line relay of the selector at the end ofthe trunk at which the trunk relay is located, a switching relay at eachend of said trunk for transferring the trunk from the windings of thetrunk relay to the windings of the line relay of the selector, and relaymeans in each of the selectors responsive to operation of the line relayfor operating said switching relay.

5. In a telephone system, a two-Way trunk, means at each end of saidtrunk for seizing said trunk on an outgoing call, a trunk relay at eachend of said trunk, said relays being normally bridged across theconductors of said trunk for operation upon seizure of the trunk at theopposite end, an incoming selector at each end of the trunk for use incompleting calls incoming over said trunk, a line relay for each of saidselectors, the operation of the trunk relay at one end of said trunkupon seizure of the trunk at the other end being effective to guard saidtrunk from seizure at said one end and to cause the operation of theline relay of the associated incoming selector, and means responsive tothe operation of said line relay for disconnecting said trunk relay fromsaid trunk and for connectingsaid line relay to said trunk.

6. In a telephone system, according to claim 5, means controlled by saidline relay for guarding said trunk from seizure at said one end.

ARTHUR B. SPERRY.

